1. Field of the Invention
The invention relates to a circuit arrangement for identifying in a color decoder, the transmission standard of a color television signal comprising a chrominance subcarrier upon which chrominance information is modulated, and synchronizing pulses.
For color television signals, there is an abundance of different transmission standards which differ from each other more specifically in the manner in which the chrominance information components are transmitted. These chrominance information components are modulated on a chrominance subcarrier which however may have different frequencies depending on the standard and which in addition may have a frequency which alternates from picture line to picture line of the color television signal. The chrominance information components themselves are also modulated in different manners. For color decoders which must be suitable for decoding color television signals of different transmission standards, this causes the problem that the color decoders must not only be suitable for decoding the different transmission standards but that they must also be capable of recognizing which transmission standard the color television signal to be decoded has.
2. Description of the Related Art
Known circuit arrangements for identifying the transmission standard of color television signals generally operate in an iterative manner, that is to say they first switch to any random standard, then check whether the color decoder is capable of decoding and switching the chrominance information components and, if not, switch to a subsequent standard. This procedure is continued until the color decoder is switched to a transmission standard for which a correct decoding of the chrominance information components of the color television signal is effected. Thus, in this procedure a given transmission standard is not immediately identified but the correct transmission standard is ultimately determined by testing different decodings. This requires a certain period of time which, particularly also in the case of short interruptions or interferences of the color television signal may be displayed in an annoying manner, since the search procedure starts again from the beginning after each interruption.